Synthesis of poly((vinyloxy)ethanesulfonic acid)-grafted ETFE membrane via radiation grafting and its characterization

We report the synthesis of a new fuel cell membrane, poly((vinyloxy)ethanesulfonic acid)‐grafted poly(ethylene‐co‐tetrafluoroethylene) (ETFE) film by simultaneous radiation grafting of 2‐chloroethyl vinyl ether onto ETFE film followed by sulfonation. The effects of various irradiation conditions such as the solvents, dose rate, and monomer concentration on the degree of grafting were investigated in detail. The sulfonation procedure of the grafted ETFE films used to replace the chlorine group with a sulfonic acid group includes the following steps. The first step is the formation of thiouronium salt with thiourea, the second step is the hydrolysis with NaOH to form thiol, and the final step is an oxidation of thiol using hydrogen peroxide to achieve the desired sulfonic acid group. Fourier transform infrared spectroscopy (FTIR), x‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy‐energy dispersive x‐ray spectroscopy (SEM–EDX) instruments were used to confirm the chemical reaction at every step of the process. In addition, the thermal degradation behaviors of the original ETFE film, grafted ETFE film, and sulfonated membrane were investigated by thermogravimetric analysis. To elucidate the possible applications of poly((vinyloxy)ethanesulfonic acid)‐grafted ETFE membranes for direct methanol fuel cells, ion exchange capacity, water uptake, proton conductivity, and methanol permeability were investigated and compared with Nafion 212. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012